The subject invention is directed toward the art of forming products from thermoplastic materials and, more particularly, to a method of forming elongated, decorative trim strip products from thermoplastic extrusions.
The invention is particularly suited for forming decorative and protective trim strips of the type used on vehicle bodies and will be described with reference thereto; however, the invention is capable of broader application and could be used for forming products of a similar nature intended for other uses.
Trim strips applied as decorative and protective elements to the exterior surface of automotive body panels have been formed using a variety of different techniques. When such trim strips are formed from thermoplastic materials, both injection molding and extrusion processes have been used. Extrusion processing is capable of extremely high production rates with relatively low tooling costs as compared to injection molding. The extrusion process does present certain significant disadvantages, however. The most significant disadvantage is that the ends of the extruded strip element typically cannot have a smoothly tapering or contoured surface as is readily obtained with the injection molding process.
A variety of different approaches have been used in an attempt to provide contoured and shaped ends on extrusion formed thermoplastic strips. For example, separately molded end pieces have been bonded to the main extruded center section. When using this technique, a noticeable joint line generally results between the molded end sections and the extruded center section. Additionally, the color matching and appearance generally differs between the end sections and the center section. This is especially pronounced when the metal flake colorants have been used. The reason for this is that the appearance of a metal flake colorant results from the orientation of the flakes in the product surface. This cannot be controlled to provide a match between the extruded elements and the molded elements.
It has also been proposed to simply reheat the thermoplastic in the end area and reform the end shape. When using such reheat processes, however, discoloration of the end section results because of the elevated temperatures to which the plastic must be subjected.